Staphylococcus aureus toxic shock syndrome toxin 1 and Streptococcus pyogenes erythrogenic toxin A modulate inflammatory mediator release from human neutrophils

Biology and management of methicillin resistant Staphylococcus aureus in cystic fibrosis

Staphylococcus aureus is one of the earliest bacteria isolated from the respiratory tract in people with cystic fibrosis (CF). Its methicillin resistant form, MRSA, has gained attention due to the rapid increase in the last decades and worse outcomes with chronic infection. In the United States, prevalence of MRSA in CF is around 27%, but is much lower (3-18%) in most other countries. Methicillin is typically genetically encoded by the mecA gene, which encodes for an alternative penicillin binding protein (PRBa). This PRBa has low affinity to β-lactams, thereby enabling growth of S. aureus in the presence of penicillinase resistant penicillins and most other β-lactams. Non-mecA positive strains of MRSA, so-called borderline resistant (BORSA) have also been described. In addition to production of toxins, the virulence of S. aureus is conferred by its adaptability allowing persistence in face of antibiotic therapies and host defense. These adaptive growth mechanisms include small colony variants, biofilms, and growth under anaerobic conditions. Several reports have described successful eradication of MRSA, yet only two randomized trials of eradication during early infection have been conducted. A list of MRSA specific antibiotics with dosing relevant to CF patients is presented here. Many of these require special dosing in people with CF. Novel antibiotics are in trials for skin and soft tissue infections and it is unclear if and when those might be available for lung infections. Thus the best strategies for MRSA would be primary prevention.

Comparison of pathogens and antibiotic resistance of burn patients in the burn ICU or in the common burn ward

BACKGROUND

This study aims to compare pathogens and their antibiotic resistances of burn patients from burn intensive care unit (ICU) or common burn ward. Of 2395 clinical samples from 63 patients in burn ICU, pathogens were detected in 1621 samples, in which 1203 strains (74.2%) were Gram negative bacteria, 248 strains (15.3%) were Gram positive bacteria, 170 strains (10.5%) were fungi. Top-4 microorganisms isolated from patients in burn ICU were Bauman's Acinetobacter (557, 34.4%), Pseudomonas aeruginosa (287.17.7%), Staphylococcus aureus (199, 12.3%) and Klebsiella pneumoniae (171, 10.5%). Of 512 clinical samples from 235 patients in common burn units, pathogens were detected in 373 samples, in which 189 (50.6%) strains were Gram negative bacteria, 150 strains (40.2%) were Gram positive bacteria, 34 strains (9.2%) were fungi. Top-4 microorganisms isolated from patients in common burn units were S. aureus (103, 27.6%), P. aeruginosa (46, 12.3%), K. pneumoniae (38, 10.2%) and Escherichia coli (32, 8.6%). Antibiotic resistance rates of pathogens isolated from clinical samples of burn patients from ICU was significantly higher than those from common units.

CONCLUSIONS

Pathogens and their antibiotic resistances are significantly different between burn ICU and common burn units. This finding has great implication for infection control in burn patients.

Eicosanoid metabolism and eosinophilic inflammation in nasal polyp patients with immune response to Staphylococcus aureus enterotoxins

BACKGROUND

Staphylococcus aureus-derived enterotoxins (SEs) have been implicated in the pathogenesis of airway inflammatory diseases, especially nasal polyposis. However, the exact role of these molecules in the regulation of eicosanoid synthesis in this pathology remains unexplored. We studied the possible impact of SE-induced immune responses on the eicosanoid production in nasal polyp (NP) patients.

METHODS

Tissue sample homogenates from NP patients, with (NP-SEs[+]) and without detectable IgE-antibodies to SEs (NP-SEs[-]; ImmunoCap system), were assayed for IL-5, myeloperoxidase, leukotriene CJD4/E4 (LTC4/D4/E4), LTB4, lipoxin A4, total IgE, and eosinophil cationic protein.

RESULTS

Inflammatory makers, eicosanoids, and total IgE were significantly increased in NP-SEs(+) compared with NP-SEs(-) tissues, with the exception of myeloperoxidase, which was similar in both groups. Eicosanoid concentrations correlated to IL-5 and eosinophil cationic protein; however, only cys-leukotriene levels correlated with IgE-antibodies to SEs, independently of allergy and asthma.

CONCLUSION

Eicosanoid synthesis is up-regulated in polyp tissue of patients with immune response to SEs and seems to be related to the inflammatory reaction induced by these enterotoxins.

Detection of circulating superantigens in an intensive care unit population

OBJECTIVE

Plasma concentrations of superantigens were measured in an intensive care unit (ICU) population and the relationship of superantigen positive rates with the presence of sepsis was investigated.

METHODS

Plasma samples were collected at least twice a week from 78 patients whose primary diagnoses were abdominal disorders (n = 27), respiratory disorders (n = 11), trauma (n = 10), burns (n = 10), cardiovascular disorders (n = 4), neurological disorders (n = 2), and others (n = 14). Five different species of superantigens, i.e., staphylococcal enterotoxins A, B, and C (SEA, SEB, and SEC), toxic shock syndrome toxin-1 (TSST-1), and streptococcal pyrogenic exotoxin A (SPEA), were measured using an enzyme-linked immunosorbent assay.

RESULTS

Significant levels of plasma superantigens were detected in 16 patients. SEA was found in seven patients, SEB in four patients, SEC in two patients, TSST-1 in six patients, and SPEA in five patients. Superantigen detection rates were 6% (1/17) in patients without systemic inflammatory response syndrome (SIRS), 0% (0/21) in SIRS patients without infection, 31% (5/16) in septic patients without shock, and 42% (10/24) in septic shock patients.

CONCLUSIONS

The presence of superantigens was confirmed in part of the ICU population. The role of superantigens in the pathogenesis of sepsis remains to be determined.

Staphylococcal and streptococcal superantigens: molecular, biological and clinical aspects

Superantigens (SAgs) include a class of certain bacterial and viral proteins exhibiting highly potent lymphocyte-transforming (mitogenic) activity towards human and or other mammalian T lymphocytes. Unlike conventional antigens, SAgs bind to certain regions of major histocompatibility complex (MHC) class II molecules of antigen-presenting cells (APCs) outside the classical antigen-binding groove and concomitantly bind in their native form to T cells at specific motifs of the variable region of the beta chain (Vbeta) of the T cell receptor (TcR). This interaction triggers the activation (proliferation) of the targeted T lymphocytes and leads to the in vivo or in vitro release of high amounts of various cytokines and other effectors by immune cells. Each SAg interacts specifically with a characteristic set of Vbeta motifs. The review summarizes our current knowledge on S. aureus and S. pyogenes superantigen proteins. The repertoire of the staphylococcal and streptococcal SAgs comprises 24 and 8 proteins, respectively. The staphylococcal SAgs include (i) the classical enterotoxins A, B, C (and antigenic variants), D, E, and the recently discovered enterotoxins G to Q, (ii) toxic shock syndrome toxin-1, (iii) exfoliatins A and B. The streptococcal SAgs include the classical pyrogenic exotoxins A and C and the newly identified pyrogenic toxins, G, H, I, J, SMEZ, and SSA. The structural and genomic aspects of these toxins and their molecular relatedness are described as well as the available 3-D crystal structure of some of them and that of certain of their complexes with MHC class II molecules and the TcR, respectively. The pathophysiological properties and clinical disorders related to these SAgs are reviewed.

Chemokine production by rat macrophages stimulated with streptolysin O from Streptococcus pyogenes

The contribution of streptolysin O (SLO) from Streptococcus pyogenes to neutrophil infiltration in inflammatory lesions was determined by production of cytokine-induced neutrophil chemoattractant (CINC)-1, -2 and -3, and macrophage inflammatory protein (MIP)-1alpha by rat macrophages stimulated with SLO in culture. Active SLO induced the production of CINCs and MIP-1alpha in dose- and time-dependent manners. These inductions were ascertained by chemokine mRNA expression in macrophages. Streptolysin S was without effect. The SLO-cholesterol complex induced the chemokine production in proportion to the residual hemolytic activity of the complex. In addition, the effects of SLO on the chemokine production were confirmed by the injection of active SLO into the preformed air pouch on the back of rats. The infiltration of neutrophils into the pouch fluid (exudate) increased steadily with a lag phase of about 2 hr. The major chemokine found in exudates was MIP-1alpha but not CINCs. In this study, it became clear that active SLO, but not the inactive one, contributed to the production of MIP-1alpha and CINCs in the conditioned medium and in exudates.

Superantigen bacterial toxins: state of the art

Superantigens (SAgs) are viral and bacterial proteins exhibiting a highly potent polyclonal lymphocyte-proliferating activity for CD4(+), CD8(+) and sometimes gammadelta(+) T cells of human and (or) various animal species. Unlike conventional antigens, SAgs bind as unprocessed proteins to invariant regions of major histocompatibility complex (MHC) class II molecules on the surface of antigen-presenting cells (APCs) and to particular motifs of the variable region of the beta chain (Vbeta) of T-cell receptor (TcR) outside the antigen-binding groove. As a consequence, SAgs stimulate at nano-to picogram concentrations up to 10 to 30% of host T-cell repertoire while only one in 10(5)-10(6) T cells (0.01-0.0001%) are activated upon conventional antigenic peptide binding to TcR. SAg activation of an unusually high percentage of T lymphocytes initiates massive release of pro-inflammatory and other cytokines which play a pivotal role in the pathogenesis of the diseases provoked by SAg-producing microorganisms. We briefly describe in this review the molecular and biological properties of the bacterial superantigen toxins and mitogens identified in the past decade.

Superantigen-dependent accelerated death of bovine neutrophilic granulocytes in vitro is mediated by blood mononuclear cells

While classical interactions of bacterial superantigens (SAgs) with antigen presenting cells and T cells have been studied intensively, the potential interactions of SAgs with granulocytes (PMNs) have gained much less attention. We investigated if in the bovine system SAgs have any direct or indirect influence on the fate of granulocytes, which are among those cells primarily responsible for the elimination of superantigen-producing bacteria. The tested SAgs (SEA, SEB) had no apparent direct effect on PMN viability (neutrophils and eosinophils). However, in the presence of blood mononuclear cells (MNCs), SAgs led to an accelerated death of neutrophils but not of eosinophils. Compared to medium controls, in SAg-stimulated cultures only about 20-50% of the neutrophils survived after 24 hours in vitro. Accelerated death of neutrophils required the presence of at least 10% MNC and started between 2.5-24 h after initiation of the co-culture between MNC and PMN. Minimal effective SEA concentrations ranged between 10-100 pg/l (SEB 0.1-10 ng/l). The effect could be mimicked by culture supernatants of SAg-stimulated MNCs, suggesting that direct cell-cell interactions are not required for the killing. In the human system, where we tested the role of TNF-alpha, an antibody specific for this cytokine was not able to abolish the death of human neutrophils. Brefeldin A, an inhibitor of golgi transport and cytokine secretion, which blocked the SAg-induced activation of bovine MNC did not abolish the killing of neutrophils. Blocking of nitric oxide generation or PGE2 synthesis also could not alter the SAg-induced killing of bovine neutrophils. The observed indirect negative effects of SAgs on neutrophils may provide new insights in mechanisms by which superantigens modulate the hosts immune response.

Structure and function of streptococcal and staphylococcal superantigens in septic shock

The pyrogenic exotoxins of Group A Streptococci and enterotoxins of Staphylococcus aureus constitute a family of related toxins that acts as "superantigens" because of their ability to stimulate large numbers of T-cell subsets. These toxins have been implicated in gastrointestinal food poisoning, toxic shock syndromes, Gram-positive sepsis, and, possibly, septic shock. There is increasing evidence that Gram-positive infections frequently coexist in septic shock and that bacterial superantigens play a major role.

Effects of staphylococcal enterotoxins on human neutrophil functions and apoptosis

Staphylococcal enterotoxins have marked effects on the properties of T cells and monocytes and have recently been reported to affect neutrophil function. In this study, we investigated the abilities of staphylococcal enterotoxins A and B and toxic shock syndrome toxin 1 to affect respiratory burst activity and to delay apoptosis in human neutrophils. When cultures containing approximately 97% neutrophils were tested, the toxins all delayed neutrophil apoptosis in a dose-dependent manner and induced the expression of FcgammaRI on the neutrophil cell surface. These effects on apoptosis and expression of FcgammaRI were largely abrogated by the addition of a neutralizing anti-gamma interferon antibody. Similarly, the effects of these toxins on phorbol ester-induced chemiluminescence were decreased after neutralization of gamma interferon. These effects on neutrophil function were mimicked by the addition of conditioned medium from peripheral blood mononuclear cells incubated with the toxins, and again, neutralizing anti-gamma interferon antibodies largely negated the effects. However, when highly purified neutrophils prepared by immunodepletion of T cells and major histocompatibility complex class II-expressing cells were analyzed, the toxins were without effect on apoptosis and FcgammaRI expression, but granulocyte-macrophage colony-stimulating factor and gamma interferon could still delay apoptosis. These data indicate that these toxins have no direct effect on neutrophil apoptosis but can act indirectly via the production of T-cell-derived and monocyte-derived cytokines. It is noteworthy that such effects are detected in neutrophil suspensions containing only 3% contamination with T cells and other mononuclear cells.

Effects of proinflammatory cytokines and bacterial toxins on neutrophil rheologic properties

OBJECTIVE

To examine the changes in neutrophil deformability, aggregation, and adherence in response to stimulation with proinflammatory cytokines and bacterial toxins.

DESIGN

Prospective, randomized trial.

SETTING

Research laboratory.

SUBJECTS

Neutrophils isolated from healthy volunteers.

INTERVENTIONS

Neutrophils were exposed to tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-8, their combination, endotoxin (LPS), lipoteichoic acid (LTA), and staphyloccocal enterotoxin B (SEB). Neutrophil deformability was measured as percent neutrophils filtered through 5-microm diameter filters. Aggregation was measured using a platelet aggregometer. Adherence was determined by examining the binding of neutrophils to albumin-coated latex beads.

MEASUREMENTS AND MAIN RESULTS

Exposure to TNF-alpha and IL-1beta led to significant decreases in neutrophil filterability, which was attenuated by cytochalasin D pretreatment. LPS and LTA also decreased deformability, suggesting that these toxins directly stimulated neutrophils independent of cytokines. IL-8 and SEB did not significantly affect neutrophil deformability. TNF-alpha and LPS were associated with significant neutrophil aggregation, which was inhibited by pretreatment with anti-CD18 antibodies. Neutrophil aggregation was not affected by IL-1beta, LTA, or SEB. TNF-alpha, IL-8, and LPS increased neutrophil adherence, which also was attenuated by pretreatment with anti-CD18 antibodies. IL-1beta, LTA, and SEB did not significantly affect neutrophil adherence.

CONCLUSIONS

Cytokines and bacterial toxins differ in their effects on neutrophil deformability, aggregation, and adherence. Of the cytokines examined, TNF-alpha appears to have the greatest direct effects on neutrophil rheology. Similarly, endotoxin appears to have greater direct effects on neutrophil rheology than the Gram-positive bacterial toxins, LTA, and staphylococcal enterotoxins.

The pathogenesis of Staphylococcus aureus in the trauma patient and potential future therapies

BACKGROUND

Staphylococcus aureus is the most frequently isolated pathogen in the trauma patient and uses multiple virulent factors to cause infection. At the cellular level, infection begins with the prokaryotic bacterial cell manipulating the eukaryotic host cell through its virulent factors. Researching this cellular interaction by describing the mechanisms of actions of various virulent factors may lead to new preventive therapies which will make the trauma patient less susceptible to S aureus infections.

METHODS

Surgical, medical, and microbial literature was reviewed to provide an update on S aureus pathogenesis.

RESULTS

Novel future therapies, in addition to antibiotics, are being devised based on understanding the molecular nature of S aureus pathogenesis.

CONCLUSION

The impact of S aureus on trauma will increase as S aureus develops more antibiotic resistance and as the trauma population becomes older and includes an increasing proportion of immunocompromised patients. To meet the challenge of increased virulence, trauma surgeons should be directly involved in the research of microbial pathogenesis.

Bacterial pyrogenic exotoxins as superantigens

The recent discovery of the mode of interaction between a group of microbial proteins known as superantigens and the immune system has opened a wide area of investigation into the possible role of these molecules in human diseases. Superantigens produced by certain viruses and bacteria, including Mycoplasma species, are either secreted or membrane-bound proteins. A unique feature of these proteins is that they can interact simultaneously with distinct receptors on different types of cells, resulting in enhanced cell-cell interaction and triggering a series of biochemical reactions that can lead to excessive cell proliferation and the release of inflammatory cytokines. However, although superantigens share many features, they can have very different biological effects that are potentiated by host genetic and environmental factors. This review focuses on a group of secreted pyrogenic toxins that belong to the superantigen family and highlights some of their structural-functional features and their roles in diseases such as toxic shock and autoimmunity. Deciphering the biological activities of the various superantigens and understanding their role in the pathogenesis of microbial infections and their sequelae will enable us to devise means by which we can intervene with their activity and/or manipulate them to our advantage.

Role of a carboxy-terminal site of toxic shock syndrome toxin 1 in eliciting immune responses of human peripheral blood mononuclear cells

Staphylococcus aureus toxic shock syndrome toxin 1 (TSST-1) is involved in the pathogenesis of toxic shock syndrome and perhaps other staphylococcal diseases. Recently, the C-terminal part of the TSST-1 toxin has been shown to be responsible for mitogenic activity in animal models. We studied the role of the C-terminal structural unit of TSST-1 with regard to proliferation, cytokine release (tumor necrosis factor alpha [TNF-alpha], interleukin-6 [IL-6], and IL-8), mRNA expression for IL-6, IL-8, IL-10, TNF-alpha, and CD40 ligand (CD40L), synthesis of immunoglobulin E (IgE), IgA, IgG, and IgM, CD23 expression, and soluble CD23 (sCD23) release from human peripheral blood mononuclear cells (PBMC). For this purpose, we used the recombinant wild-type TSST-1 (p17) mutant toxin Y115A (tyrosine residue modified to alanine) and toxin H135A (histidine residue modified to alanine). Unmodified toxin p17 and mutant toxin Y115A, at a concentration below 5 ng, to a lesser degree, induced a strong proliferation. Toxin p17 followed by toxin Y115A was the most pronounced inducer for mRNA expression for IL-10 and CD40L and cytokine generation (mRNA and protein) for TNF-alpha, IL-6, and IL-8. Mutant protein H135A failed to activate human PBMC. Both toxins p17 and, to a lesser degree, Y115A significantly suppressed IL-4- and anti-CD40-induced synthesis of all four Igs as well as IL-4-induced CD23 expression and sCD23 release. Mutant toxin H135A failed to do so. Thus, our data show that a region in the C terminus of TSST-1 is responsible not only for mitogenic activity but also for additional immunomodulating biological activities of TSST-1. More specifically, histidine residue H135A of the 194-amino-acid toxin appears to be critical for the expression of biological activities in a human in vitro model.

Activation of human effector cells by different bacterial toxins (leukocidin, alveolysin, and erythrogenic toxin A): generation of interleukin-8

We analyzed the transcription and release of interleukin-8 (IL-8) from human polymorphonuclear granulocytes (PMNs) and a lymphocyte-monocyte-basophil (LMB) cell population stimulated for different time periods (30 min to 16 h) with pore-forming bacterial toxins (Panton-Valentine leukocidin [Luk-PV] and alveolysin [Alv]) as well as with the erythrogenic toxin A (ETA) as a superantigen. At high toxin concentrations (500 ng/10(7) cells), Luk-PV and Alv led to a decreased IL-8 generation from LMBs within the first 30 min; with PMNs, a slight increase in IL-8 release was observed. Under these conditions, stimulation with ETA did not lead to an altered cellular IL-8 release. At lower concentrations (5 and 0.5 ng/10(7) cells), all three toxins led to a continuous increase (over 16 h) in IL-8 release and IL-8 mRNA expression of PMNs and LMBs. Preincubation of the cells with the protein tyrosine kinase inhibitors lavendustin A and tyrphostin 25 led to a reduction of the toxin-mediated effects on IL-8 release and IL-8 mRNA expression when Luk-PV and Alv were used as stimuli. In contrast, IL-8 synthesis in cells which were stimulated with ETA was not influenced by protein tyrosine kinase inhibition. From our data, one may suggest that multiple pathways for IL-8 production are operative in human leukocytes.